Vehicle input shafts are used to transmit drive power from an engine to a drive line through a clutch assembly. The first end of the vehicle input shaft is typically received within a bearing of a flywheel attached to the crank of the engine. This arrangement stabilizes the center point of rotation of the vehicle input shaft. One or more clutch plates or discs are mounted near the first end of the vehicle input shaft for axial movement along the shaft, while preventing relative rotation between the input shaft and the clutch disc(s). The second end of the vehicle input shaft is typically drivingly connected with the drive line of the vehicle, e.g., through a transmission assembly.
Conventional vehicle input shafts include drive teeth that engage the clutch disc(s) to allow the disc(s) to move axially along the shaft while preventing relative rotational movement. The drive teeth are provided in the form of splines having grooves therebetween that exit out onto the central cylindrical portion of the shaft, creating a stress riser at the location where the splines meet the cylindrical shaft. This is characteristically the location where current input drive shafts experience failure. In addition, current input shafts have cylindrical bearing bosses with end tapers that do not allow the bosses to move freely when they flex from the extreme side loads experienced during use. These design flaws cause current input shafts to fail after a limited amount of use.